Vaillant ecoTEC plus Fault codes & diagnostics

121 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

SystemCombi Natural Gas 10-40 kW 2023-present
GC Number 41-694-45

The ecoTEC plus range comes in 3 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

Download the Vaillant ecoTEC plus manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 100 High 15 Medium 4 Low

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-694-45 ecoTEC plus 610 VU 10CS/1-5 (N-GB) 2023–present

All 121 documented codes

Tap any card for details

con

Your boiler's control panel and its internal computer are not talking to each other, meaning the unit cannot receive instructions to provide heat or hot water.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Display Interface Module
  • Wiring harness

Related codes

F.000

Your boiler has lost its connection to a temperature probe, meaning it cannot tell how hot the water is and has stopped working for your safety.

High Engineer only £120-200

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness
  • PCB

Related codes

F.001

Your boiler has lost its connection to the sensor that measures how hot the water is as it flows back into the unit, forcing it to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.002

Your boiler has lost the connection to the sensor that measures the temperature of your hot water, so it cannot currently provide hot water to your taps or shower.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC sensor
  • Wiring harness

Related codes

F.003

Your boiler has lost the connection to the temperature sensor in your hot water cylinder, so it doesn't know when your hot water is up to temperature.

Medium Engineer only £120-220

Parts commonly replaced

  • Cylinder NTC sensor
  • Wiring harness
F.010

Your boiler has detected a faulty signal from a heat sensor, causing it to stop heating your home as a safety precaution.

High Engineer only £120-200

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

F.011

Your boiler has detected an electrical fault in a sensor that measures the temperature of water returning to the unit, causing it to stop working for safety reasons.

High Engineer only £120-220

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.012

Your boiler is having difficulty reading the temperature of the water being heated for your taps, which will likely prevent you from getting hot water.

Medium Engineer only £120-200

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Thermistor
  • Wiring harness

Related codes

F.013

Your boiler has lost the ability to read the temperature of your hot water tank because of a faulty connection or sensor.

Medium Engineer only £120-200

Parts commonly replaced

  • Cylinder NTC sensor
  • Wiring harness

Related codes

F.020

Your boiler has automatically shut down because it reached a dangerously high temperature to prevent damage to the internal components.

High Engineer only £150-300

Parts commonly replaced

  • NTC Temperature sensor
  • Pump (heating circulation)
  • Printed Circuit Board (PCB)

Related codes

Showing 11–20 of 121
F.022

Your boiler has stopped working because the water pressure inside your heating system has dropped too low to operate safely.

High DIY-safe £80-120

What to check first

  1. Locate the external filling loop (a silver flexi-hose) connected to the pipework underneath your boiler.
  2. Slowly open the valve(s) on the loop to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly and check the boiler display to see if the fault code has cleared.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel

Related codes

F.023

Your boiler has detected that the water leaving it is much hotter than the water returning, suggesting a blockage or a problem with the pump circulating the water efficiently.

High Engineer only £180-350

Parts commonly replaced

  • Central heating pump
  • System filter
  • Heat exchanger

Related codes

F.024

Your boiler is shutting down because the water inside it is heating up much faster than it can be moved around your radiators, suggesting a flow issue.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • System filter
  • Heat exchanger

Related codes

F.025

Your boiler has detected that the exhaust gases leaving the unit are hotter than they should be, so it has shut down to protect itself from overheating.

High Engineer only £150-350

Parts commonly replaced

  • NTC temperature sensor
  • Heat exchanger
  • Flue gas limit switch

Related codes

F.027

Your boiler is confused and thinks it is still burning gas even though it has told itself to switch off, which is a safety lockout to prevent accidental ignition.

Emergency Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

F.028

Your boiler is failing to light the internal burner, meaning you currently have no heating or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

F.029

Your boiler has stopped working because it is not receiving a reliable supply of gas or the flame keeps going out.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Printed Circuit Board

Related codes

F.032

Your boiler is struggling to breathe properly because the internal fan that pushes air out is not spinning at the correct speed.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
F.035

Your boiler is struggling to breathe because the pipe that vents exhaust gases outside is blocked or obstructed.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue terminal
  • Air pressure switch
  • Fan assembly

Related codes

F.040

Your boiler is struggling to get the right balance of air for a clean burn, which prevents it from igniting safely.

High Engineer only £150-300

Parts commonly replaced

  • Venturi
  • Gas valve
  • Fan assembly
  • Air intake seal

Related codes

Showing 21–30 of 121
F.042

Your boiler has lost the digital instructions telling it how to configure itself for your specific heating system, preventing it from starting up safely.

High Engineer only £150-300

Parts commonly replaced

  • Coding resistor
  • Main printed circuit board (PCB)
F.044

Your boiler is struggling to detect the flame needed to heat your water and home, so it has shut down to stay safe.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame rectification lead
  • Printed Circuit Board (PCB)

Related codes

F.047

Your boiler is struggling to understand the temperature of the water being sent to your hot water tank because it is receiving an illogical reading from a sensor.

Medium Engineer only £120-220

Parts commonly replaced

  • Hot water cylinder sensor
  • Wiring harness

Related codes

F.049

Your boiler's communication wires are experiencing a wiring conflict or short circuit, which is preventing the system from sending signals correctly.

High Engineer only £120-250

Parts commonly replaced

  • eBUS connection terminals
  • Main PCB
  • Communication wiring harness
F.057

Your boiler has detected a critical issue with its internal combustion control system that it cannot fix itself, so it has shut down for your safety.

High Engineer only £250-450

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Ionisation probe

Related codes

F.061

Your boiler's internal computer is failing to start up or communicate correctly, which has caused the system to shut down for safety.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness

Related codes

F.062

Your boiler is struggling to confirm that the flame has turned off as quickly as it should have, which means it has stopped working for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Printed circuit board (PCB)

Related codes

F.063

Your boiler's computer is struggling to store or read its internal settings properly, which prevents it from starting up safely.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

F.064

Your boiler has detected an internal error where it can no longer accurately read the temperature or pressure data it needs to operate safely.

High Engineer only £150-250

Parts commonly replaced

  • NTC temperature sensor
  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

F.065

Your boiler has detected that one of its internal electronic parts is running far too hot and has shut itself down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • NTC thermistor

Related codes

Showing 31–40 of 121
F.067

Your boiler is unable to safely detect whether the burner flame is lit, so it has shut itself down to prevent a safety hazard.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Flame rectification probe

Related codes

F.068

Your boiler is struggling to detect the flame reliably, so it has turned itself off to stay safe, meaning you currently have no heating or hot water.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • Printed circuit board

Related codes

F.070

Your boiler’s internal computer is confused because it cannot correctly identify the specific hardware model it is currently installed in.

High Engineer only £120-250

Parts commonly replaced

  • Coding resistor
  • Main printed circuit board (PCB)

Related codes

F.071

Your boiler's internal thermometer is sending conflicting temperature readings to the control board, so the system has shut down to prevent damage.

High Engineer only £150-250

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness

Related codes

F.072

Your boiler is struggling because it cannot detect a normal temperature difference between the water leaving and returning to the unit, suggesting the system is not circulating heat correctly.

High Engineer only £150-300

Parts commonly replaced

  • NTC Temperature sensors
  • Central heating pump
  • Primary heat exchanger

Related codes

F.074

Your boiler has lost the ability to read your central heating water pressure because the connection to its internal monitoring sensor has failed.

Medium Engineer only £120-220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

F.075

Your boiler is struggling to detect the movement of water when it tries to start the heating, which usually means the internal pump is failing to spin or there is a blockage preventing flow.

High Engineer only £250-450

Parts commonly replaced

  • Circulation pump
  • Pressure sensor
  • PCB

Related codes

F.076

Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage to its internal parts.

High Engineer only £150-300

Parts commonly replaced

  • NTC sensor
  • Primary heat exchanger
  • Pump

Related codes

F.077

Your boiler has detected an issue with the drainage system or flue safety mechanism, so it has safely stopped working to prevent potential water damage or combustion faults.

High Engineer only £120-250

Parts commonly replaced

  • Condensate pump
  • Flue non-return valve
  • PCB

Related codes

F.078

Your boiler's electronic brain is having trouble communicating with an external control accessory, preventing the system from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • eBUS adapter
  • PCB
  • External heating controller

Related codes

Showing 41–50 of 121
F.080

Your boiler is struggling to accurately measure the temperature of the water coming into your home, which may result in your hot water not being heated to the correct temperature.

Medium Engineer only £120-220

Parts commonly replaced

  • Cold water inlet sensor
  • Wiring harness (if damaged)

Related codes

F.081

Your boiler is struggling to pump hot water into your hot water cylinder, which means you may have no hot water available.

High Engineer only £150-300

Parts commonly replaced

  • Diverter valve
  • Diverter valve motor
  • NTC sensor

Related codes

F.083

Your boiler is failing to heat up the water properly when it tries to start, so it has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • NTC temperature sensors
  • Heating pump
  • Diverter valve

Related codes

F.084

Your boiler is confused because it detects a strange temperature difference between the water leaving the boiler and the water coming back, causing it to shut down to protect itself.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature sensors
  • Pump
  • Main PCB

Related codes

F.085

Your boiler's temperature sensors have been fitted incorrectly or have become misaligned, preventing the system from accurately reading the water temperature.

High Engineer only £120-200

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness
F.087

Your boiler has lost the internal electrical connection needed to spark and light the burner, meaning it cannot produce any heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition transformer
  • Wiring harness
  • Main PCB

Related codes

F.088

Your boiler has lost the internal connection needed to control the gas supply, which prevents it from igniting and heating your home.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve wiring harness
  • Gas valve
  • Main printed circuit board (PCB)

Related codes

F.089

Your boiler has detected that the internal water pump is not the correct version required for this specific model, preventing the system from circulating heat properly.

High Engineer only £250-450

Parts commonly replaced

  • High-efficiency circulation pump
  • PCB

Related codes

F.090

Your boiler has lost its digital connection to the hot water cylinder, meaning it currently doesn't know how to heat your stored water.

High Engineer only £150-300

Parts commonly replaced

  • eBUS communication cable
  • VR 10 sensor
  • Main PCB

Related codes

F.092

Your boiler has detected that the settings controlling how it uses gas were not finalized correctly during its last setup or maintenance, which prevents it from firing up safely.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
Showing 51–60 of 121
F.095

Your boiler is having trouble managing its internal gas flow, which is preventing it from firing up reliably.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve assembly
  • Printed Circuit Board (PCB)

Related codes

F.096

Your boiler has detected that a small internal component responsible for regulating the gas flow is stuck or worn out, which prevents it from safely igniting.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Main PCB

Related codes

F.097

Your boiler's internal computer has flagged a self-test failure, meaning it cannot safely control its operations and will remain shut down to prevent damage.

High Engineer only £300-500

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

F.105

Your boiler has detected an internal communication error with the gas control system, meaning it cannot safely regulate the fuel supply to operate.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
F.194

Your boiler's internal electronic control center is failing to receive a consistent power signal, which is preventing the system from operating safely.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

F.195

Your boiler has detected that the incoming electricity supply is too weak to run the system safely.

High Engineer only £120-250

Parts commonly replaced

  • Internal wiring harness
  • Main printed circuit board (PCB)
F.196

Your boiler has detected an unstable or too-high electrical voltage coming from your home's power supply, causing it to shut down for protection.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Power supply module

Related codes

F.317

Your boiler is having trouble detecting exactly how much hot water you are using, which means it may struggle to heat your water properly.

Medium Engineer only £150-250

Parts commonly replaced

  • Flow sensor
  • Wiring harness
  • Printed Circuit Board

Related codes

F.318

Your boiler is struggling to switch between heating your radiators and heating your hot water because the internal diverter valve is stuck in one position.

High Engineer only £180-350

Parts commonly replaced

  • Diverter valve actuator head
  • Diverter valve cartridge
  • Wiring harness

Related codes

F.320

Your boiler's water circulation pump is stuck or jammed, preventing heat from being moved around your home.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Pump head

Related codes

Showing 61–70 of 121
F.321

Your boiler's water pump has encountered an internal communication error, meaning it cannot circulate heat to your radiators or taps.

High Engineer only £250-450

Parts commonly replaced

  • Pump assembly
  • Pump electronics module
  • Main PCB

Related codes

F.322

Your boiler’s internal water pump has become too hot and the system can no longer safely circulate heat, causing the boiler to shut down to prevent damage.

High Engineer only £250-450

Parts commonly replaced

  • Central heating pump
  • Pump wiring harness
  • Printed Circuit Board

Related codes

F.323

Your boiler has detected that the water pump inside is spinning without being fully submerged in water, preventing it from circulating heat around your home.

High Engineer only £150-350

Parts commonly replaced

  • Circulation pump
  • Pressure relief valve
  • Air vent

Related codes

F.324

Your boiler has lost the electrical connection needed to keep its internal water pump running, so it has safely shut down to prevent overheating.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Pump wiring harness
  • Main printed circuit board (PCB)

Related codes

F.325

Your boiler has detected that the water pump responsible for circulating heat to your radiators and taps has stopped working correctly.

High Engineer only £250-450

Parts commonly replaced

  • Central heating pump
  • Pump wiring harness
  • Printed Circuit Board

Related codes

F.326

Your boiler has detected that multiple internal valves or pumps are failing to respond, which means it cannot safely move water around the system to provide heating or hot water.

High Engineer only £250-450

Parts commonly replaced

  • Diverter valve
  • Pump
  • Main printed circuit board (PCB)

Related codes

F.327

Your boiler has detected that it is set up to provide hot water to a storage tank that isn't currently connected, causing it to limit how much water flows through your heating system.

Medium Engineer only £120-200

Parts commonly replaced

  • Main PCB
  • System configuration jumper

Related codes

F.330

Your boiler's water circulation pump is failing to start as expected, which means the system cannot safely move heat to your radiators or taps.

High Engineer only £200-400

Parts commonly replaced

  • Central heating pump
  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

F.334

Your boiler is failing to start because it cannot detect the correct setup of its exhaust pipe system.

High Engineer only £120-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Air pressure switch
  • Main printed circuit board (PCB)

Related codes

F.336

Your boiler has identified that its internal settings do not match the physical components installed, which usually happens after a recent repair or incorrect parameter configuration.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Gas valve

Related codes

Showing 71–80 of 121
F.337

Your boiler has detected that the flue system installed is incompatible with its internal setup, meaning it cannot safely vent exhaust gases.

High Engineer only £150-300

Parts commonly replaced

  • Flue adapter
  • Air intake seal
  • Main PCB

Related codes

F.338

Your boiler has detected that the settings controlling its flue system do not match the physical installation, preventing it from operating safely.

High Engineer only £120-250

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Flue sensor

Related codes

F.342

Your boiler is struggling to bring in the right amount of air needed to burn fuel correctly, so it has safely shut down to prevent any issues.

High Engineer only £150-350

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Flue system components

Related codes

F.343

Your boiler's air-flow sensor is failing to provide a consistent reading, preventing the unit from safely igniting.

High Engineer only £180-350

Parts commonly replaced

  • Air mass flow sensor
  • Wiring harness
  • Main PCB

Related codes

F.344

Your boiler has detected an internal communication error and has safely shut down because it cannot accurately monitor or control the burner process.

High Engineer only £180-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

F.347

Your boiler is unable to drain away the water it creates during normal operation, so it has safely shut itself down to prevent internal damage.

High Engineer only £100-200

Parts commonly replaced

  • Condensate trap
  • Condensate siphon
  • Drain pipework

Related codes

F.363

Your boiler's computer is having trouble saving or reading its internal memory settings, which prevents it from operating correctly.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Display Interface Module

Related codes

F.707

Your boiler's control panel and its internal computer are failing to talk to each other, which prevents the system from starting.

High Engineer only £150-300

Parts commonly replaced

  • Main electronic control board (PCB)
  • Communication cable/wiring harness
  • User interface display

Related codes

F.905

Your boiler's electronic control panel is experiencing an electrical overload, which has caused it to temporarily stop talking to the heating system to protect itself.

High Engineer only £150-350

Parts commonly replaced

  • eBUS PCB
  • Wiring harness
  • Display interface
L.016

Your boiler has shut down because the flame went out unexpectedly while it was running at its lowest setting.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Flame detector electrode
  • Printed Circuit Board

Related codes

Showing 81–90 of 121
L.022

Your boiler has detected that there is not enough water circulating through your heating system to work properly.

High DIY-safe £80-150

What to check first

  1. Check your boiler pressure gauge to see if it is below 1.0 bar.
  2. Locate the filling loop (usually a silver braided hose with a tap underneath the boiler).
  3. Open the tap slowly to top up the system pressure until the needle reaches between 1.0 and 1.5 bar, then turn it off tightly.

Parts commonly replaced

  • Central heating pump
  • System pressure sensor
  • Flow sensor

Related codes

L.025

Your boiler is having difficulty reading the temperature of the incoming cold water, which may prevent it from heating your water correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • Cold water NTC sensor
  • Wiring harness

Related codes

L.032

Your boiler is struggling to accurately measure the speed of the water circulating inside it, which will prevent your heating and hot water from working correctly.

High Engineer only £180-300

Parts commonly replaced

  • Flow sensor
  • Wiring harness

Related codes

L.095

Your boiler is struggling to control its gas flow properly, meaning it cannot maintain a stable flame to heat your water or home.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve assembly
  • PCB

Related codes

L.096

Your boiler's gas control mechanism has reached its operational adjustment limit, meaning it can no longer properly balance the fuel and air mix to heat your home safely.

High Engineer only £200-350

Parts commonly replaced

  • Gas valve
  • Gas valve stepper motor

Related codes

L.097

Your boiler is struggling to mix the right amount of air with the gas it uses to create a flame, which means it has safely shut itself down to prevent inefficient burning.

High Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Venturi
  • Air intake seal
  • Fan

Related codes

L.105

Your boiler has failed to remove air from its internal system during the start-up process, meaning it cannot begin heating your water safely.

High Engineer only £120-250

Parts commonly replaced

  • Automatic air vent
  • Pressure sensor
  • Pump

Related codes

L.144

Your boiler is struggling to detect the flame correctly, so it has turned itself off to stay safe and prevent gas from building up.

High Engineer only £150-250

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • Main PCB

Related codes

L.194

Your boiler has detected an internal electrical fault within its control system, which is preventing it from starting up correctly.

High Engineer only £250-450

Parts commonly replaced

  • PCB
  • Main control board
  • Power supply module

Related codes

L.195

Your boiler is receiving insufficient power from your home's electrical supply, which is preventing it from operating correctly.

High Engineer only £120-250

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness

Related codes

Showing 91–100 of 121
L.196

Your boiler has detected that the incoming electricity supply is at a dangerously high voltage, so it has shut itself down to protect its internal electronics from being permanently fried.

High Engineer only £150-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Surge protection device

Related codes

L.319

Your boiler is struggling to push water around your heating system because a path that allows internal water flow has become restricted or blocked.

High Engineer only £150-300

Parts commonly replaced

  • Bypass valve
  • Diverter valve
  • System filter

Related codes

L.320

Your boiler's water pump is stuck, so the system is trying to clear the obstruction automatically before it stops working entirely.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Pump head

Related codes

L.322

Your boiler has detected that the internal water pump component is getting too hot, so it has safely shut down to prevent further damage.

High Engineer only £200-450

Parts commonly replaced

  • Circulation pump
  • Pump wiring harness
  • Printed Circuit Board (PCB)

Related codes

L.343

Your boiler is struggling to accurately measure the airflow needed for safe combustion, so it has safely shut down to prevent incorrect operation.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure sensor
  • Venturi
  • Fan assembly
  • Main PCB

Related codes

N.013

Your boiler's internal sensor that detects how much water is inside is currently sending a confusing signal, so the system has stopped working to stay safe.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

N.027

Your boiler is struggling to accurately measure the temperature of the water being heated for your taps and shower, likely due to a faulty sensor or a loose wire.

Medium Engineer only £120-220

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Thermistor
  • Wiring harness

Related codes

N.032

Your boiler is struggling to accurately measure the water flowing through it, which is preventing it from heating your water safely.

High Engineer only £180-300

Parts commonly replaced

  • Volume flow sensor
  • Wiring harness

Related codes

N.089

Your boiler has detected that the internal water pump is not the correct type for your specific model, preventing the system from circulating water properly.

High Engineer only £250-450

Parts commonly replaced

  • High-efficiency circulation pump
  • PCB (Printed Circuit Board)

Related codes

N.095

Your boiler is having trouble controlling the flow of gas accurately, which means it cannot safely or efficiently ignite, resulting in a loss of heating and hot water.

High Engineer only £200-350

Parts commonly replaced

  • Gas valve
  • PCB

Related codes

Showing 101–110 of 121
N.096

Your boiler's gas control mechanism is struggling to function correctly, preventing the unit from igniting or maintaining a steady flame.

High Engineer only £200-350

Parts commonly replaced

  • Gas valve
  • Gas valve stepper motor

Related codes

N.097

Your boiler is struggling to mix the right amount of air with its gas supply to burn fuel efficiently.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Venturi
  • Fan assembly

Related codes

N.100

Your boiler has lost the connection to the thermometer placed outside your home, so it can no longer automatically adjust your heating based on the weather.

Low Engineer only £90-180

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring loom
N.144

Your boiler is struggling to detect the flame needed to heat your home, and it has tried and failed to adjust itself automatically.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

N.194

Your boiler's internal computer is failing to receive a stable electrical supply, which means the unit cannot start or operate.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Power supply unit

Related codes

N.270

Your boiler has detected that hot water is not transferring correctly through its internal heating system, so it is limiting its own performance to prevent further stress.

High Engineer only £150-350

Parts commonly replaced

  • Plate-to-plate heat exchanger
  • Diverter valve
  • System filter

Related codes

N.317

Your boiler is struggling to detect if water is flowing through your hot water pipes, which usually means it cannot start heating your water properly.

Medium Engineer only £150-250

Parts commonly replaced

  • Domestic hot water flow sensor
  • Wiring harness

Related codes

N.319

Your boiler is struggling to circulate water effectively because an internal safety valve is stuck or blocked, which may cause it to turn itself off to prevent overheating.

Medium Engineer only £150-250

Parts commonly replaced

  • Internal bypass valve
  • Diverter valve

Related codes

N.324

Your boiler has lost the internal connection to the water pump, meaning it is currently unable to circulate heat to your radiators or taps.

High Engineer only £150-300

Parts commonly replaced

  • Pump wiring harness
  • Central heating pump
  • Main PCB

Related codes

N.343

Your boiler is struggling to accurately measure the air it needs for combustion, so it is running in a limited state to remain operational.

Medium Engineer only £150-250

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Showing 111–120 of 121
S.032

Your boiler is struggling to maintain the correct airflow required to burn gas safely and is automatically restarting its internal fan to rectify the issue.

High Engineer only £150-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

S.041

Your boiler has detected that the water pressure inside your heating system is currently too high for it to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate a radiator in your home with a bleed valve.
  2. Using a radiator key, slightly open the valve to release a small amount of air and water into a cloth or container.
  3. Close the valve once water begins to trickle out steadily.
  4. Monitor the boiler's pressure gauge until it returns to the green zone (typically between 1.0 and 1.5 bar).

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Pressure sensor

Related codes

S.042

Your boiler is temporarily pausing its operation because a safety device connected to the heating system is signaling that it cannot safely exhaust or drain properly.

Medium Engineer only £120-250

Parts commonly replaced

  • Condensate pump
  • Flue non-return flap
  • PCB

Related codes

S.054

Your boiler has detected low water pressure and is currently in a waiting period before it attempts to restart.

High DIY-safe £80-120

What to check first

  1. Locate the filling loop (a silver flexi-hose) underneath the boiler or near your pipework.
  2. Open the valves on the hose to let mains water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.0 to 1.5 bar).
  4. Close the valves firmly and check that the fault code clears.

Parts commonly replaced

  • Pressure sensor
  • Filling loop valve

Related codes

S.057

Your boiler has temporarily stopped working because it detected an issue with the combustion process and is now safely waiting before attempting to restart.

High Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Flue gas analysis sensor
  • Printed Circuit Board (PCB)

Related codes

S.059

Your boiler is ready to heat your home, but it cannot currently pump enough water around the system to safely turn the flames on.

High DIY-safe £120-250

What to check first

  1. Check that all radiator valves throughout your home are fully open
  2. Inspect the boiler pressure gauge to ensure it is between 1 and 1.5 bar
  3. If the pressure is below 1 bar, use the filling loop to top it up to the correct level

Parts commonly replaced

  • Central heating pump
  • System filter
  • Flow sensor

Related codes

S.096

Your boiler is currently running a set of automatic internal diagnostic checks and has temporarily paused heating and hot water to ensure everything is working correctly.

Low Engineer only £100-200

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness
  • Main PCB

Related codes

S.097

Your boiler is currently running a quick internal safety check on its pressure sensor and has paused heating while it finishes.

Low Engineer only

Parts commonly replaced

  • Water pressure sensor
  • Main PCB

Related codes

S.098

Your boiler is currently running a routine internal health check on its temperature sensors and has temporarily paused heating to complete the scan.

Low Engineer only £100-200

Parts commonly replaced

  • NTC temperature sensor
  • PCB

Related codes

Showing 121–121 of 121
S.599

Your boiler has detected an internal software or communication error and has safely paused operation to prevent further issues.

High Engineer only £120-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Communication cable

Related codes

160 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

D.000 Diagnostic Your boiler is currently set to run at a lower power level than its maximum capacity to save energy or match your home's heat demand. D.001 Diagnostic Your boiler's internal water pump is staying on longer than expected, which is usually just a temporary communication glitch between the system components. D.002 Diagnostic Your boiler is currently in a mandatory waiting period to prevent it from switching on and off too frequently, which is a normal part of its operation. D.003 Diagnostic This code is simply a status message showing the current temperature of the water being heated for your taps and shower, rather than an indication of a fault. D.004 Diagnostic Your boiler is struggling to accurately detect the temperature of your stored hot water, which may cause your hot water to be inconsistent or unavailable. D.005 Diagnostic Your boiler is simply reporting the current temperature it has been instructed to heat your radiators to, which is a normal operational status rather than a fault. D.006 Diagnostic Your boiler is currently monitoring or adjusting the temperature setting for your hot water, which is a normal part of its internal operation. D.008 Diagnostic Your boiler is receiving a signal from your thermostat that it is currently calling for heat, so it is simply showing you that your heating system is active. D.009 Diagnostic Your boiler is receiving an unusual signal from your thermostat or controls, which is preventing it from knowing exactly how much heat to produce. D.010 Diagnostic Your boiler is currently reporting that the internal pump, which moves water around your radiators, is experiencing a communication or operation signal issue. D.011 Diagnostic Your boiler is simply indicating that an external pump connected to your heating system is currently running or receiving a signal to operate. D.012 Diagnostic Your boiler is currently running a process to heat your hot water storage tank. D.013 Diagnostic Your boiler is notifying you that it is currently monitoring the internal water pump to ensure it is running correctly. D.015 Diagnostic Your boiler is simply reporting the current speed at which your internal water pump is running to circulate heat through your radiators. D.016 Diagnostic Your boiler is struggling to receive the signal from your wall-mounted thermostat to turn on the heating. D.017 Diagnostic Your boiler has detected an issue with how the central heating controls are communicating with the heating system. D.018 Diagnostic Your boiler is simply indicating that the internal water pump is currently running to circulate heat through your radiators. D.020 Diagnostic Your boiler is currently displaying its setting for the maximum hot water temperature rather than indicating a fault. D.021 Diagnostic Your boiler is simply indicating that the 'warm start' feature, which keeps a small amount of water pre-heated for faster hot water taps, is currently active. D.022 Diagnostic Your boiler is simply detecting a request for hot water and is operating exactly as it should. D.023 Diagnostic Your boiler is currently waiting for a signal from your thermostat or timer to tell it to start heating your home or water. D.025 Diagnostic Your boiler is simply indicating that it has received a signal from your controls to heat the water for your taps or shower. D.026 Diagnostic Your boiler has detected an issue with an internal electrical switch that controls optional accessories, which may prevent your heating or hot water from turning on correctly. D.027 Diagnostic Your boiler is struggling to communicate with an external add-on device, such as a remote control, a separate water pump, or a timer. D.028 Diagnostic Your boiler is struggling to communicate with an external add-on device, such as a remote heating controller or a secondary pump, and cannot activate it as expected. D.029 Diagnostic Your boiler is struggling to pump water around your radiators effectively, often because the flow of water is being restricted. D.031 Diagnostic Your boiler has detected an issue with its built-in system that automatically keeps the water pressure at the correct level. D.033 Diagnostic Your boiler is struggling to reach or maintain the correct fan speed, which means it cannot vent exhaust gases properly and will stop working to keep you safe. D.034 Diagnostic Your boiler is having trouble communicating with its internal fan, which is preventing the system from starting safely. D.035 Diagnostic Your boiler is struggling to switch between heating your radiators and heating your hot water because the internal diverter valve is stuck or not responding. D.036 Diagnostic Your boiler is struggling to detect the water flow needed to provide hot water, often because the flow sensor is clogged or faulty. D.039 Diagnostic Your boiler is struggling to accurately detect the temperature of the cold water entering the system, which may affect how well it heats your hot water tap supply. D.040 Diagnostic Your boiler is simply reporting the current temperature of the water flowing through the system, and this code is just a status notification rather than a breakdown. D.041 Diagnostic Your boiler is struggling to accurately measure the temperature of the water returning to it from your radiators. D.043 Diagnostic Your boiler is displaying a setting related to how it adjusts its heat output based on the outdoor temperature, and this is typically an informational notification rather than a broken part. D.045 Diagnostic Your boiler is flagging an issue with the settings that determine how much heat it produces based on the outdoor temperature. D.047 Diagnostic Your boiler is struggling to read the temperature from the sensor installed outside your home, so it is defaulting to a standard heating mode. D.052 Diagnostic Your boiler is struggling to correctly control the amount of gas flowing into the burner, meaning it cannot safely ignite or maintain a steady flame. D.058 Diagnostic Your boiler is currently drawing heat from your solar thermal system to help warm up your water, which is a normal part of how your system functions. D.060 Diagnostic Your boiler has detected that it has overheated multiple times in the past and is now flagging this recurring issue to prevent internal damage. D.061 Diagnostic Your boiler has failed to start up several times in a row, so it has locked itself for safety to prevent gas buildup. D.062 Diagnostic Your boiler is simply indicating that it is currently operating in its programmed night-time energy-saving mode, which is a normal status rather than a fault. D.064 Diagnostic Your boiler is struggling to light the burner smoothly, taking longer than it should to establish a flame. D.065 Diagnostic Your boiler is failing to light the flame during the startup process. D.066 Diagnostic Your boiler's 'warm start' feature, which keeps a small amount of water pre-heated for faster hot water taps, is experiencing a communication or activation issue. D.067 Diagnostic Your boiler is currently in a mandatory waiting period to prevent it from switching on and off too frequently, which is a normal safety feature to protect the system. D.068 Diagnostic Your boiler is failing to start up because it has tried and failed to light the flame several times in a row. D.069 Diagnostic Your boiler has failed to light the burner twice in a row, so it has safely stopped trying to prevent wasting fuel. D.070 Diagnostic Your boiler is struggling to switch between providing hot water and heating your radiators because a internal motorized valve is stuck or not responding. D.071 Diagnostic Your boiler is temporarily limiting the heat of the water it produces to prevent the system from getting too hot while it regulates itself. D.072 Diagnostic Your boiler is simply moving excess heat away from the hot water tank to ensure the system cools down safely after a heating cycle. D.073 Diagnostic Your boiler is having a minor disagreement with the setting used to keep a small amount of water pre-heated for your taps. D.074 Diagnostic Your boiler is currently performing a routine high-temperature cycle to kill bacteria in your hot water cylinder, which is a normal and automatic safety feature. D.075 Diagnostic Your boiler is struggling to heat your hot water tank, taking too long to reach the desired temperature, which usually points to a sensor issue or a blockage in the flow. D.077 Diagnostic Your boiler is momentarily operating at its maximum power output to heat your water, which is a standard status message rather than a breakdown. D.078 Diagnostic Your boiler is currently monitoring or limiting the temperature of your hot water supply to ensure it stays within a safe, pre-set range. D.080 Diagnostic This code is simply an information display showing the total number of hours your boiler has spent running the central heating system. D.081 Diagnostic This code is simply an information display showing the total number of hours your boiler has spent heating your hot water, not a fault with the system. D.082 Diagnostic Your boiler is simply showing you that it is currently in the process of starting up to provide heat to your radiators. D.083 Diagnostic Your boiler is currently performing a routine internal check as it prepares to heat your hot water, which is a normal part of its operation. D.084 Diagnostic Your boiler is simply reminding you that it is time for its annual safety service. D.085 Diagnostic Your boiler is currently running at its lowest power setting to maintain a stable flame, which is a normal operational state rather than a malfunction. D.088 Diagnostic Your boiler is struggling to detect enough water flowing through the system to safely turn on your hot water tap. D.090 Diagnostic Your boiler is having trouble communicating with its external controller or smart thermostat, which is preventing it from receiving proper instructions to heat your home. D.091 Diagnostic Your boiler is struggling to receive the wireless radio signal that automatically updates its internal clock. D.092 Diagnostic Your boiler is having difficulty communicating with your hot water storage cylinder, which means it may struggle to provide consistent hot water. D.093 Diagnostic Your boiler has lost its unique digital identity, which prevents it from knowing how to correctly manage your heating and hot water settings. D.094 Diagnostic Your boiler's history log has been cleared, which is a maintenance action rather than a sign of a physical problem. D.095 Diagnostic Your boiler is simply displaying a notification regarding the version of its internal software and is not indicating a mechanical fault. D.096 Diagnostic Your boiler has lost its specific configuration settings and needs to be re-calibrated by a professional to ensure it operates correctly. D.098 Diagnostic Your boiler's electronic brain is struggling to recognise the specific settings for your unit because a small plug-in component has become loose or faulty. D.124 Diagnostic Your boiler is simply displaying a status message indicating that a smart energy-saving feature is currently active and functioning correctly. D.125 Diagnostic Your boiler is struggling to accurately measure the temperature of the hot water being sent to your taps, which may cause your hot water to fluctuate or stop working entirely. D.128 Diagnostic Your boiler has detected that the water temperature is struggling to reach the level required to keep your home warm, likely due to a flow issue or a sensor communication error. D.129 Diagnostic Your boiler is struggling to register the correct temperature settings for your hot water, which may lead to your taps not getting as hot as they should be. D.145 Diagnostic Your boiler has detected that the exhaust pipe or air intake is blocked, preventing it from operating safely. D.146 Diagnostic Your boiler has detected that the ignition electrode, which helps light the flame, has reached its operational life limit and needs replacing to ensure the boiler continues to work reliably. D.147 Diagnostic Your boiler has detected an issue with the sensor responsible for managing the ignition process and monitoring the flame, and it requires a professional service to resolve. D.156 Diagnostic Your boiler is currently in a setup mode and is waiting for a professional to configure it for the specific type of gas being used in your home. D.157 Diagnostic Your boiler's electronic brain is currently unsure which type of gas is being supplied to it, causing the system to lock out for your protection. D.158 Diagnostic Your boiler is struggling to correctly mix the gas and air needed for combustion, which prevents it from firing up safely. D.159 Diagnostic Your boiler is currently waiting for a short period before restarting to prevent it from cycling on and off too frequently. D.160 Diagnostic Your boiler is struggling to accurately read or maintain the required internal water pressure level. D.161 Diagnostic Your boiler is simply reminding you that its annual service is now due to ensure it continues to run safely and efficiently. D.162 Diagnostic Your boiler is struggling to communicate with the external weather sensor that adjusts your heating automatically based on the outdoor temperature. D.163 Diagnostic Your boiler has detected an issue with an external add-on component, such as an external pump or secondary heating controller, which is preventing it from operating as intended. D.164 Diagnostic Your boiler has detected that the flue system is set up for a single-pipe configuration, which is a standard internal setting rather than a breakdown. D.166 Diagnostic Your boiler's electronic control system is experiencing an internal communication error and cannot safely operate its gas-burning components. D.167 Diagnostic Your boiler is having difficulty communicating with your hot water cylinder, which may mean you will have no hot water until the connection is restored. D.170 Diagnostic Your boiler is currently performing an internal configuration check or system update, which usually happens after it has been switched on or had its settings adjusted. D.171 Diagnostic Your boiler is struggling to detect the correct water pressure inside the system, which may be caused by a sensor issue or an imbalance in the water levels. D.172 Diagnostic Your boiler is currently monitoring a mismatch between the desired temperature and the actual temperature of the water flowing through your heating system. D.173 Diagnostic Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely. D.174 Diagnostic Your boiler has detected that the water pressure inside the heating system has risen to a dangerously high level. D.175 Diagnostic Your boiler is struggling to detect or control the speed of the pump that pushes water around your heating system. D.182 Diagnostic Your boiler is having difficulty communicating with the gas control system, which means it cannot safely ignite the flame to heat your water or home. D.185 Diagnostic Your boiler is struggling to recognise its own internal setup, which usually happens if a settings change was recently attempted or the main control board has lost its stored configuration. D.186 Diagnostic Your boiler is struggling to communicate with the shared flue system used in your building, preventing it from starting safely. D.187 Diagnostic Your boiler is currently in a setup mode and is waiting for a professional to finalize the configuration of your flue system settings. I.003 Diagnostic Your boiler has reached its programmed service interval and is kindly reminding you that it is time for its annual health check. I.020 Diagnostic Your boiler's water pressure has dropped too low, which is stopping it from circulating heat effectively around your home. I.144 Diagnostic Your boiler’s internal ignition sensor is showing signs of age and needs to be replaced to ensure the unit continues to light reliably. P.000 Diagnostic Your boiler is currently running an automatic air-clearing sequence, which is a normal process after maintenance or a power restart. P.2 Diagnostic Your boiler is currently running a background self-test to check it can operate safely at its lowest power setting. P.008 Diagnostic Your boiler is currently undergoing an automatic system fill or internal pressure adjustment process. S.0 Status Your boiler is working perfectly fine and is simply in standby mode because your thermostat is not currently asking for the heating to be turned on. S.000 Status Your boiler is currently in standby mode because it has not received a request from your thermostat or hot water timer to start heating. S.1 Status Your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber. S.001 Status Your boiler is simply preparing to start the heating process and you do not need to take any action. S.2 Status Your boiler is currently moving water through the system after a heating or hot water cycle to cool down the internal components safely. S.002 Status Your boiler is simply preparing to heat your home and is currently getting the water moving before the burners light up. S.003 Status Your boiler is operating normally and is currently firing up to provide heat to your home. S.4 Status Your boiler is operating normally and is currently in the process of starting up the burner to provide heat or hot water. S.004 Status Your boiler is operating normally and is currently heating your radiators. S.005 Status Your boiler is currently taking a moment to cool down or finish its internal circulation cycle after the heating has been running. S.006 Status Your boiler is currently just finishing its normal cooling cycle after being in use, so everything is working exactly as it should. S.7 Status Your boiler is briefly keeping the internal pump running to safely circulate and dissipate leftover heat after you have finished using your heating or hot water. S.007 Status Your boiler is simply finishing its normal cooling cycle after providing heating to your radiators. S.008 Status Your boiler is working perfectly fine; it is currently in a brief, automatic resting period to prevent it from turning on and off too frequently. S.009 Status Your boiler is performing a normal, automatic maintenance check on its internal sensors to ensure it continues to run efficiently. S.10 Status Your boiler is simply letting you know that it is currently busy heating up water for your taps or shower. S.010 Status Your boiler is currently in standby mode because it has not detected a request for hot water or heating. S.11 Status Your boiler is simply preparing its internal airflow to heat your water, which is a normal part of its startup process and not an error at all. S.011 Status Your boiler is currently operating normally as it prepares to heat water for your taps or shower. S.012 Status This is a normal operational status message indicating your boiler is preparing to provide hot water, not a fault code. S.013 Status Your boiler is working exactly as it should and is currently heating up water for your taps or shower. S.014 Status Your boiler is currently heating your hot water, which is a normal part of its everyday operation. S.15 Status Your boiler is simply performing a routine cooling-down process after you last used hot water, and there is no fault with your system. S.015 Status Your boiler is currently processing a request for hot water and is just finishing its normal shutdown process; this is a standard operating status and not a fault. S.016 Status Your boiler is currently running the internal fan to safely vent gases after you have just used your hot water taps. S.17 Status Your boiler is simply finishing its cooling cycle after you have finished using hot water, and no action is required. S.017 Status Your boiler is currently working correctly to provide hot water, and the system is simply clearing out residual heat after the tap was turned off. S.019 Status Your boiler is simply performing a routine internal self-calibration process while you are using hot water, and no action is required. S.20 Status Your boiler is not broken; it is simply letting you know that it has received a request to provide hot water and is currently preparing to deliver it. S.020 Status Your boiler is currently in a standby state because it has not received a request to heat your hot water storage tank. S.021 Status Your boiler is currently heating up the hot water in your storage tank and restarting the fan to facilitate this process. S.022 Status Your boiler is currently heating up the internal hot water storage tank and is simply preparing its internal pump for the task. S.023 Status Your boiler is currently heating up the water stored in your hot water cylinder, which is a normal part of its routine operation. S.024 Status Your boiler is operating normally and has successfully finished heating up your hot water storage tank. S.025 Status Your boiler is currently busy heating up your hot water storage tank and is running its internal components to finish that task. S.026 Status Your boiler is currently heating the water stored in your hot water tank and is finishing its cooling cycle, which is a normal part of its operation. S.027 Status Your boiler is currently heating up the water for your hot water storage tank and finalizing a standard operation cycle. S.028 Status Your boiler is currently waiting to restart after heating up your hot water storage tank, which is a normal part of its operation. S.029 Status Your boiler is simply performing a quick, automatic self-check to ensure its internal sensors remain accurate while heating up your hot water cylinder. S.030 Status Your boiler is currently in standby mode because it has not received a request for heat from your home's thermostat or timer. S.031 Status Your boiler is currently in standby mode because it has not been asked to provide any heating or hot water, and is operating exactly as it should. S.034 Status Your boiler is temporarily running its pump to prevent the water inside from freezing during cold weather. S.039 Status Your boiler is currently unable to detect the water flow needed to heat your home because the external flow sensor is not registering any movement. S.088 Status Your boiler is currently running a brief automatic process to clear trapped air from the system after being restarted or serviced. S.091 Status Your boiler is currently stuck in a demonstration mode used for showrooms and is not operating as a normal home heating appliance. S.092 Status Your boiler is currently running a routine automated check to ensure there is enough water flowing through the system, so no action is required while this temporary process completes. S.093 Diagnostic Your boiler is currently performing a routine self-check and is temporarily unable to complete the test that monitors the quality of the exhaust gases. S.109 Status Your boiler has temporarily stopped working because it has entered a standby mode, usually while it waits for a signal from your thermostat or because it needs to take a short break before restarting. S.199 Status Your boiler is currently refilling its internal water levels automatically to ensure it has enough pressure to operate correctly. S.326 Diagnostic Your boiler is currently performing a brief automatic safety test on its internal water systems, which is a normal part of its operating cycle. S.328 Status Your boiler's external water pump is staying on all the time, even when the heating isn't requested, which is usually due to a wiring or settings error during installation. S.335 Status Your boiler is currently performing a safety check to ensure exhaust gases can safely escape through the flue. S.341 Status Your boiler is simply taking a short break from running at full power because it has been working hard for a long period, and it will resume normal operation automatically. T.001 Diagnostic Your boiler is struggling to circulate water because the internal pump is not working as expected, which will prevent your heating and hot water from functioning. T.007 Diagnostic Your boiler is currently operating at its lowest possible power setting, which is a normal state and not an error code requiring repair.

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